Trying to get my Nextcloud 12 to integrate with my PERSONAL ONLYOFFICE account...

It works only one way. I can create a doc in ONLY OFFICE PERSONAL and it appears in my NC 12. To go the other way, NC > ONLYOFFICE I need the document server address?? The ONLYOFFICE app is installed correctly in NC...

It should work in one direction. Your NC12 instance should be connected to your own ONLYOFFICE Document Server instance. ONLYOFFICE PERSONAL cannot be used for the integration with your NC. You cannot integrate ONLYOFFICE PERSONAL document editing service into any third party application.